LDAP: Detect the presence of POSIX attributes
When the schema is set to AD and ID mapping is not used, there is a one-time
check ran when searching for users to detect the presence of POSIX
attributes in LDAP. If this check fails, the search fails as if no entry
was found and returns a special error code.
The sdap_server_opts structure is filled every time a client connects to
a server so the posix check boolean is reset to false again on connecting
to the server.
It might be better to move the check to where the rootDSE is retrieved,
but the check depends on several features that are not known to the code
that retrieves the rootDSE (or the connection code for example) such as what
the attribute mappings are or the authentication method that should be used.
Reviewed-by: Sumit Bose <email@example.com>
Reviewed-by: Pavel Březina <firstname.lastname@example.org>
(cherry picked from commit e81deec535d11912b87954c81a1edd768c1386c9)